Color photography



Oei. 9;, 1923.

.1.16. CAPSTAFF COLOR PHOTOGRAPHY Filed July 12. 1922 l f, ./M

ATTORNEYS.`

@5 to the image therate a JOHN G. CAPSTAFF, OF ROCHESTER, NEW'YOBK, ASSIGNOB TO EASTMAN KODAKVCOM- PANY, OF ROCHESTER, NEW YORK, A CORPORATION-0F NEW YORK.

COLOR PHOTOGRAPHY.

Application medJuly 12, 1922. Serial No. 574,363.

c and State of New York, have invented certain new and useful lmprovements in Color Photography, of which the following is a full. clear, and exact specifica-tion.

'lfhis invention relates to improvements in lo the -art oil color photography, and particulai-ly to certainV steps in the making of color component images which are to be viewed in su rposition. i

uch a process is described in my Patent le 1,196,080, granted Aug. 29th,'1916, which process in brief consists of the making of color component negatives through complementary hlters, submitting the resultant silver images to a bleaching-tanning bath,

d e- 2c ino the resultant bleached images, the 'dye being adsorbed diderentially and inversely to the silver image, and superposing the ima s.

l ave discovered that when an image obl25 tained by bleachin in the manner described in the patent is su mitted tothe action of a dye of the ty@ there mentioned that the resulant dye image is formed, developed or built up ina manner analogous to the forma- 30 tion or development of a photographic image as developed from a latent image, and l have applied this discoveryto the techni ue of making color pictures that are we l balanced through a wide scale of tones.

As iS well known, the density of a developed image is 'not directly proportional to the time of development but is rather l a logarithmic function of that time. v Moreover, as is alsowell known, the contrast in the developed image, denoted in photographic literature by gamma, increases with development, there being for any particular set of lphotographie conditions, a value gamma infinity, at which the image E is fully developed; and if development is pushed further, it results in a substantially uniform increase of density and usually in the introduction of general fog as a result of the development of particles over the 50, entire sensitized area, and particularly in the less exposed areas.

Analogously, when a bleached image of the nature mentioned is submitted to the action of an appropriate d e, dye is adsorbed nd extent of adsorption bein analogous to the action of development escribed. The dye does not tint the photographic vemulsioiinor thai-mage therein uniformly nor proportionally to the' time, but builds up a dye image in which the contrast, which may be called thedye-gamnia, increases to a maximum which may be called dye-gammafintinity when the dye image is fully formed.

lf dyeing is carried beyond the dyegamma-innity stage the dye image is built up in density without materially adecting gamma, though it builds up particularly in the high lights.

.If dyeing is stopped before 'that stage there results an image of less desit and of lower dye-gamma than the ful y dyed image. f

It will thus be seenthat the action is uite analogous to that of development. l ave applied the discovery of this vproperty tothe formation and control of the images of a multi-color process. Other conditions bevivpg the same, the gamma ot a silver image vary with the color ofithe light by which the camera exposure was made. ln particular, color component images made through a red filter will have a higher gamma than those made through a reen lter. By properly controlling the yeing oit the bleached images made by m patented process, it is possible to contro the color v what clearer by reference to the accompanying `figures comprising a series of diagrams illustrating characteristic curves' the images at various stepsin the process.

Fig. 1 represents an ideal negative;

Fig. 2 an ideal positive; l

Fig. 3 two color-filter nega-tives;

Fig. e two dye positives corresponding to the silver images of Fig. 3;

Fig. 5 two color-filter negatives balanced for the high-lights; and

Fig 6 the dye images made by dierentially dyeing bleached images corresponding to the silver images of Figs. 5'.

These diagrams, it is to understood, are made as simply as ossible. ln' practice the curvesare not straight lines, as here shown, but are more or less curved, their form depending on' the particular emulsion, developer, exposure, temperature, dye baths, land El@ Qro other factors used in the particular circumstances.

llt will be assumed that the subgect to be photographed includes neutral objects, 'each redecting ual amounts of red and green light, but t at the objects have diderent brightnesses. 'llhe photographic silver negative image including such objects, Whether taken by green light, red light or red and green light, should represent 'them by a series of densities proportional to the logarithm of their brightness. Fig. 1 the characteristic curve of such a negative image is shown, the density ol? the several points A, D, C, and D being plotted against the lo arit of their brightness, A being very ark, and D very light. The corre'- sponding positive image would yield a line having a reverse slope, as shown in Fig. 2,

Awhere density of image is plotted against the logarithm of the original subject brightnem. lf a color image including such sub- Tjects comprises two colored complementary images made from exposures taken through red and green filters it is obvious the slopes of theircharacteristic lines should be the Vln practice, however, has been `iol-1nd i that images taken by red light will have a.

greater slope than those taken by green light, other photographic factors beingthe same. ln Fig. 3, are lshown the curves Vllt and G for two 'negative images, resulting from ual exposures by red and green light vEi@ till

respectively, and including a series of neutral objects of diderent brightness,l the density of the several points as produced byred light being indicated by AR, BR, CR and DR, and the density of the images as produced by reen light being indicated by AG, BG, Chg and DG. lf these images were bleached and tanned in accordance with my above mentioned patent and then dyed equally, the points could be plotted as shown in F ig. 4l, the green filter image being dyed red and 'the red' filter image dyed green. The shadows would have a greenish tinge Vsince AG is greater than AR and the high lights a reddish tinge since DR is greater than DG and since, as stated ih my patent, the dye is adsorbed didcrentially and inversely to the density of the original silver image. 'lhe green dye image of A is deeper than the red dye image; and the red dye image of D deeper than the green image.

. lin my discovery of the fact that dye images change their slopes as they are built up, l have a means'whereby the dierence's 1n their 'slope may be controlled and balanced. lf the dye image'having the normally higher slope is built-up to a less extent, .the slope of the two images will be the same, and it they have the same depthor characteristic line :Maasai in lFi. It is built up to a less extent, its s ope wi be the vsame as that of r and it will be parallel thereto but lower; that is, the picture as a wholev will have a reddish tinge. The slopes would be'.

Fig. 6, in the high lights, and if the dye images were fully developed, the green dye image, made by dyeing green the bleached red filter silver ima e, would have a steeper characteristic line than would the other image. The dyeing of this image is therev fore stopped at the point where its images have been built up to the same extent as the-red dyed bleached reen filter image and both fall on the line' `G and are balanced throughout. a

As noted above the actual practice is not as simple as the theoretical considerations indicate, partl because of the variations in the shapes ctv the curves, which are not straight lines and cannot be made .t0 balance absolutely Athroughout their length. However the principles outlined above determine a method of controlling the curves. lln motion picture practice .the exposures are made and from these master positives are printed. From these master positives-y on opposite surfaces of a double coated ilm.

This is described in myprior patent.

The dryness of the lm affects the density 'llhis defect may be corrected byv the curves will intersect at dRG,

but not the slope of the' dye image. As 1t.

is customary to dye one side of the film, then dry it; then dye the other side and dey the hlm again, it is important that the dryness of the lm at the times of dyeing e controlled.

The several colored image layers may be assembled to form a transparency. or they may be formed in coatings already in posif tion on opposite surfaces of a film, this being my preferred method. A very great advantage ot this method is that it throws much of the corrective control into the final tepv so that errors that may not have been discovered can be corrected by variations in the dye bath. lt is possible to carry along the printing stepsof the process by standard methods and exercise the-control bg the' tinal dyeing-step at a time when t e complete color image is being formed.

v extent, be compensated for by the methods herein described, particularly when. combined with variations in the intermediate' printing steps, which in such cases would be A so timed and proportioned as to bringtheA .characteristics of the final silver images as nearly as possible to the preferred relation. Having thus described my invention,

what l claim as new and desire to secure by Letters Patent is:

l 1. In the art of color photography wherein color component silver images aire made and severally transformed into complementary dye images, the improvements that *comprise the formation of. the Silver images- With different-characteristics of density and contrast, and carrying thevtransformation to di'erent stages of completeness to com pensate 'for the differences in ch'aracteristics.

2. The method of producingcolor picv tures comprising the making of complementa sca es and dyeing them diferentially', the dye images being built up to different extents to compensate for the different conl trast scales of the original images.

' responding tothe image having the less cony "-10 ltrast and less density being built up to a.

greater extent `than the other.

4. The method of producing color* piccolor images having different contrast tures comprising the production upon oposite sides of a transparent support of diferent color-component photographic images having different. contrast scales, and then dyeing the two images different colors, the extent of the dyeing of the images being controlled in accordance with the contrast scale of the respective images.

5. In the art of color photography in which two complen'ientarycolor component silver photographic images are formed in registry upon o posite surfaces of a film, and then treatedp to render the images differentially adsorptive of dye, and then dyeing them incomplementary colors, the iniprovements comprising, first, the formation of the twov series-of silver images with different contrast' and density characteristics, and, second, the controlled differential dye- `ver photographic images are formed in registry upon vopposite surfaces of a film as a result 4of exposure and development, 'and then are treated to produce images that are differentially adsorptive of dye,yand then dyeing such images in complementaryl colors, the improvements that' comprise, first, the control of the ratio of the two exposures so that one image will be denser than, the other, and, second, the differential dyein accor ance with the difference in t eir original densities. v

\Signed, at Rochester, New York, this 8th -day of-July, 1922. l

JOHN Gr. CAPSTAFF.

of these images after tr tment inv '60 ing of these images, after bleaching, so as I 

